Biological specimens, such as tissue sections from human subjects, can be treated with a stain containing an organic fluorophore conjugated to an antibody which binds to protein, protein fragments, or other targets in the specimen. The stained specimen is then illuminated with light and the fluorophore fluoresces. A digital camera attached to a microscope is used to capture an image of the specimen. The areas where the fluorophore/antibody combination are bound to the target of interest (e.g., protein produced by cancerous cells) appear as colored regions in the image of the specimen, with the color of the area being dictated by the fluorescence spectrum of the fluorophore applied to the specimen. In addition to the visible spectrum, the fluorescence signal may be detected in the infrared or ultraviolet regions, depending on the emission spectrum of the particular fluorophore. A stain containing two or more fluorophores can also be applied to the specimen. These methods have a variety of uses, including diagnosis of disease, assessment of response to treatment, and development of new drugs to fight disease.
More recently, quantum dots have been developed as a detection material for biological staining and imaging applications. Quantum dots (Qdot™ nanocrystals or Qdots™) are nano-crystalline luminescent semiconductor materials. Quantum dots provide several advantages over traditional organic fluorophores for use in biological staining applications. These advantages include narrow emission band peaks, broad absorption spectra, intense signals and relative fluorescent signal stability. However, the fluorescence intensity of quantum dots and quantum dot conjugates in solution is historically unstable if stored under incompatible conditions.